In prior known antenna constructions intended for personal radio communication devices it has been striven for a radiation pattern as symmetric as possible in order to that the position of the telecommunication device would not have an effect on the quality of a radio connection. The symmetry of the radiation pattern is however only realized in a free space. Various obstacles in the vicinity of a radio communication device have an effect on the radiation pattern of an antenna. Personal radio communication devices are at present so small that for example in radio telephones in which the microphone is integrated in the radio telephone, the antenna is, when in the operating position of the telephone, so close to the body that the body has an effect on the radiation pattern of the antenna. Radiation pattern is not symmetric in the typical operating positions of a radio telephone if the radio telephone is small-size and the antenna comes very close to the head and hand of the user of the telecommunication device.
It has been striven for to reduce the effect of the body on the radiation pattern and on the other hand to reduce the radiation towards the body using solutions, in which the radiation is attenuated or the form of the radiation pattern is changed using different shields placed between the antenna and the body. Also such solutions are prior known, in which it is striven for to move the radiating antenna element as far as possible from the user of the telephone. These solutions however are rather difficult to realize if a radio telephone is of very small size.
It has to be noticed that international standardizing organizations are defining measuring methods and limits for the radiation of the transmitters of mobile telephones directed towards the body of the users of mobile telephones, and accordingly it has to be accounted for in antenna designing. The radiation is measured in operating positions typical of a telephone using so called SAR--measuring (Specific Absorbtion Rate). The subject has to be paid attention to especially in the handphones of a cellular network, which operate at a rather high transmitting output power compared with the size of the telephone, such as AMPS, GSM, DCS and in the future UMTS. The radius of a cell, i.e. the maximum distance from the telephone to the nearest base station, is in these systems normally several kilometers, even up to tens of kilometers, and the transmitter output power of the handphone is up to 2 W.
The size of personal mobile stations is being continuously reduced, due to which the using of prior known antenna solutions is becoming more difficult. The problems of prior known solutions become evident with a particular emphasis, if a radio telephone is fastened rigidly to the body, e.g. with a strap on a user's wrist. In such a case both the effect of the hand on the antenna, and in the operating position the effect of the head on the antenna should be minimized.
In prior known technique it has been presented antenna solutions for pagers intended for fastening on the hand. A pager, however, does not comprise a transmitter, but only a receiver, and accordingly the radiation of the antenna towards the body does not cause a problem with pagers. Additionally, the operating position of a pager is different. In the operating position a pager is not brought close to the head, as is the case with a wristband telephone. In some antennas of wristband pagers it has though been striven for to reduce the effect of the hand on the antenna, but not that of the head. In addition to above in pagers it has been striven for an antenna direction pattern with as good a coverage to every direction as possible.
Also the requirements of a mobile telephone network on an antenna used in a telephone have to taken into account. A connection between a mobile telephone and a base station is a two-way connection, and thus the base station of the mobile telephone network has to be capable of receiving the signal transmitted by the mobile telephone. When a mobile telephone is placed in a wristband, or it is for some other reason desired to make a mobile telephone as small as possible, a transmitter cannot be designed to be very powerful in order to secure a connection. Using a transmitter with a higher output power would result in the need of a bigger power supply (battery), in which case a telephone would become large and heavy, and very difficult to place on the wrist. Thus the requirements on the antenna of a radio telephone are much stricter than on the antennas of such devices which only comprise a receiver. In radio broadcast receiver and pager systems transmitters are fixed, and accordingly they can be large, and in addition to it the power supplies are connected to mains voltage and thus the transmitters can be overdimensioned and correspondingly compromises can be made on the quality of the reception antennas.